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.TH GETPRIORITY 3C "Apr 1, 2008"
.SH NAME
getpriority, setpriority \- get and set the nice value
.SH SYNOPSIS
.LP
.nf
#include <sys/resource.h>

\fBint\fR \fBgetpriority\fR(\fBint\fR \fIwhich\fR, \fBid_t\fR \fIwho\fR);
.fi

.LP
.nf
\fBint\fR \fBsetpriority\fR(\fBint\fR \fIwhich\fR, \fBid_t\fR \fIwho\fR, \fBint\fR \fIvalue\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBgetpriority()\fR function obtains the nice value of a process, thread,
or set of processes.  The \fBsetpriority()\fR function sets the nice value of a
process, thread, or set of processes to \fIvalue\fR+\fBNZERO\fR, where
\fBNZERO\fR is defined to be 20.
.sp
.LP
Target entities are specified by the values of the \fIwhich\fR and \fIwho\fR
arguments.  The \fIwhich\fR argument can be one of the following values:
\fBPRIO_PROCESS\fR, \fBPRIO_PGRP\fR, \fBPRIO_USER\fR, \fBPRIO_GROUP\fR,
\fBPRIO_SESSION\fR, \fBPRIO_LWP\fR, \fBPRIO_TASK\fR, \fBPRIO_PROJECT\fR,
\fBPRIO_ZONE\fR, or \fBPRIO_CONTRACT\fR, indicating that the \fIwho\fR argument
is to be interpreted as a process ID, a process group ID, an effective user ID,
an effective group ID, a session ID, a thread (lwp) ID, a task ID, a project
ID, a zone ID, or a process contract ID, respectively.  A 0 value for the
\fIwho\fR argument specifies the current process, process group, or user. A 0
value for the \fIwho\fR argument is treated as valid group ID, session ID,
thread (lwp) ID, task ID, project ID, zone ID, or process contract ID. A
\fBP_MYID\fR value for the \fIwho\fR argument can be used to specify the
current group, session, thread, task, project, zone, or process contract,
respectively.
.sp
.LP
If a specified process is multi-threaded, the nice value set with
\fBsetpriority()\fR affects all threads in the process.
.sp
.LP
If more than one process is specified, \fBgetpriority()\fR returns \fBNZERO\fR
less than the lowest nice value pertaining to any of the specified entities,
and \fBsetpriority()\fR sets the nice values of all of the specified processes
to \fIvalue\fR+\fBNZERO\fR.
.sp
.LP
The default nice value is \fBNZERO\fR. Lower nice values cause more favorable
scheduling. The range of valid nice values is 0 to \fBNZERO\fR*2-1. If
\fIvalue\fR+\fBNZERO\fR is less than the system's lowest supported nice value,
\fBsetpriority()\fR sets the nice value to the lowest supported value. If
\fIvalue\fR+\fBNZERO\fR is greater than the system's highest supported nice
value, \fBsetpriority()\fR sets the nice value to the highest supported value.
.sp
.LP
Only a process with appropriate privileges can lower the nice value.
.sp
.LP
Any process or thread using \fBSCHED_FIFO\fR or \fBSCHED_RR\fR is unaffected by
a call to \fBsetpriority()\fR. This is not considered an error. A process or
thread that subsequently reverts to \fBSCHED_OTHER\fR will not have its
priority affected by such a \fBsetpriority()\fR call.
.sp
.LP
The effect of changing the nice value varies depending on the scheduling policy
in effect.
.sp
.LP
Since \fBgetpriority()\fR can return the value -1 on successful completion, it
is necessary to set \fBerrno\fR to 0 prior to a call to \fBgetpriority()\fR. If
\fBgetpriority()\fR returns the value -1, then \fBerrno\fR can be checked to
see if an error occurred or if the value is a legitimate nice value.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fBgetpriority()\fR returns an integer in the range
from -\fBNZERO\fR to \fBNZERO\fR-1.  Otherwise, \fB\(mi1\fR is returned and
\fBerrno\fR is set to indicate the error.
.sp
.LP
Upon successful completion, \fBsetpriority()\fR returns \fB0\fR. Otherwise,
\fB\(mi1\fR is returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.sp
.LP
The \fBgetpriority()\fR and \fBsetpriority()\fR functions will fail if:
.sp
.ne 2
.na
\fB\fBESRCH\fR\fR
.ad
.RS 10n
No process or thread could be located using the \fIwhich\fR and \fIwho\fR
argument values specified.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value of the \fIwhich\fR argument was not recognized, or the value of the
\fIwho\fR argument is not a valid process ID, process group ID, user ID, group
ID, session ID, thread (lwp) ID, task ID, project ID, or zone ID.
.RE

.sp
.LP
In addition, \fBsetpriority()\fR may fail if:
.sp
.ne 2
.na
\fB\fBEPERM\fR\fR
.ad
.RS 10n
A process was located, but neither the real nor effective user ID of the
executing process match the effective user ID of the process whose nice value
is being changed.
.RE

.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 10n
A request was made to change the nice value to a lower numeric value and the
current process does not have appropriate privileges.
.RE

.SH EXAMPLES
.LP
\fBExample 1 \fRExample using \fBgetpriority()\fR
.sp
.LP
The following example returns the current scheduling priority for the process
ID returned by the call to \fBgetpid\fR(2).

.sp
.in +2
.nf
#include <sys/resource.h>
\&...
int which = PRIO_PROCESS;
id_t pid;
int ret;

pid = getpid();
ret = getpriority(which, pid);
.fi
.in -2

.LP
\fBExample 2 \fRExample using \fBsetpriority()\fR
.sp
.LP
The following example sets the nice value for the current process to 0.

.sp
.in +2
.nf
#include <sys/resource.h>
\&...
int which = PRIO_PROCESS;
id_t pid;
int value = -20;
int ret;

pid = getpid();
ret = setpriority(which, pid, value);
.fi
.in -2

.SH USAGE
.sp
.LP
The \fBgetpriority()\fR and \fBsetpriority()\fR functions work with an offset
nice value (\fIvalue\fR-\fBNZERO\fR). The nice value is in the range 0 to
2*\fBNZERO\fR-1, while the return value for \fBgetpriority()\fR and the third
parameter for \fBsetpriority()\fR are in the range -\fBNZERO\fR to
\fBNZERO\fR-1.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
Standard	See \fBstandards\fR(7).
.TE

.SH SEE ALSO
.sp
.LP
.BR nice (1),
.BR renice (1),
.BR sched_get_priority_max (3C),
.BR sched_setscheduler (3C),
.BR attributes (7),
.BR standards (7)
